From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S932343AbdK0RJS (ORCPT <rfc822;w@1wt.eu>);
        Mon, 27 Nov 2017 12:09:18 -0500
Received: from mx1.redhat.com ([209.132.183.28]:33326 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1753027AbdK0RJQ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 27 Nov 2017 12:09:16 -0500
Date: Mon, 27 Nov 2017 18:09:11 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Namhyung Kim <namhyung@kernel.org>, David Ahern <dsahern@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Milind Chabbi <chabbi.milind@gmail.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Hari Bathini <hbathini@linux.vnet.ibm.com>,
        Jin Yao <yao.jin@linux.intel.com>, Kan Liang <kan.liang@intel.com>,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Oleg Nesterov <onestero@redhat.com>, Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 4/6] hw_breakpoint: Factor out
 __modify_user_hw_breakpoint function
Message-ID: <20171127170911.GA22026@krava>
References: <20171127162133.21163-1-jolsa@kernel.org>
 <20171127162133.21163-5-jolsa@kernel.org>
 <20171127164639.3ymnc6io3eae7n4c@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171127164639.3ymnc6io3eae7n4c@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.9.1 (2017-09-22)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 27 Nov 2017 17:09:16 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 27, 2017 at 05:46:39PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 27, 2017 at 05:21:31PM +0100, Jiri Olsa wrote:
> > +static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
> > +{
> > +	u64 old_addr = bp->attr.bp_addr;
> > +	u64 old_len  = bp->attr.bp_len;
> > +	int old_type = bp->attr.bp_type;
> > +	bool modify  = attr->bp_type != old_type;
> > +	int err = 0;
> > +
> > +	bp->attr.bp_addr = attr->bp_addr;
> > +	bp->attr.bp_type = attr->bp_type;
> > +	bp->attr.bp_len  = attr->bp_len;
> > +
> > +	err = validate_hw_breakpoint(bp);
> > +	if (!err && modify)
> > +		err = modify_bp_slot(bp, old_type);
> > +
> > +	if (err) {
> > +		bp->attr.bp_addr = old_addr;
> > +		bp->attr.bp_type = old_type;
> > +		bp->attr.bp_len  = old_len;
> > +		return err;
> > +	}
> > +
> > +	bp->attr.disabled = attr->disabled;
> > +	return 0;
> > +}
> 
> I think this function is failing to check if anything else in the attr
> changes.
> 
> For example, someone could have added PERF_SAMPLE_BRANCH_STACK. That's
> something you'll fail to create breakpoints with, but this modification
> would 'accept'.
> 

hum, I dont think so.. the only things you're allowed to change
are bp_addr, bp_type and bp_len.. we put new values in those
fields and keep the rest untouched.. apart from 'disabled' bit

jirka